According to the present invention, air is dehumidified by direct contact with a water-absorbing liquid. An aqueous solution of easily soluble salts such as, for example, potassium acetate, sodium acetate, potassium carbonate, calcium chloride, lithium chloride, lithium bromide and the like or mixtures thereof is suitably used as the absorption liquid. These concentrated salt solutions exhibit great affinity to water. Consequently, the water vapor pressure above the solution, is correspondingly low.
If air at a certain temperature and a certain relative humidity is brought into contact with such a concentrated salt solution, water vapor from the air is absorbed by the solution as long as the salt concentration results in a lower water vapor pressure than that present during the state of equilibrium.
When air is dehumidified by absorption of water vapor, the absorption liquid will become increasingly diluted by the absorbed water. As the only volatile component of the absorption liquid is water, it can be regenerated by evaporation. This is usually accomplished by heating the absorption liquid to a temperature at which the water vapor pressure thereof exceeds the atmospheric pressure or pressure surrounding it thus causing the water to evaporate. Concentrated salt-water solutions suitable for absorption purposes exhibit a high boiling point elevation. Generally, the dilution of the absorption liquid by absorption of water vapor is relatively small. Consequently, evaporation in more than one stage or effect is usually not feasible so that the diluted absorption liquid is usually regenerated by evaporation in a single stage evaporator.
To regenerate the absorption liquid in an evaporator an amount of energy corresponding to the heat of vaporization is required. Additional energy is needed to heat the liquid to its boiling temperature and to compensate for heat losses and the like.
The present invention utilizes the low water vapor pressure above a concentrated water-salt solution to absorb a saturated water vapor in the salt solution at a higher temperature.
According to the present invention, an absorption liquid which is used in an absorber having one or more absorption stages or zones in an air conditioning system is cooled by a circulating water stream in a heat exchanger. The water stream which takes up and carries away heat from the heat exchanger is caused to expand at reduced pressure, for example, in a flash tank. An amount of water vapor corresponding to the temperature drop, i.e. the absolute pressure is then released. The water vapor released by expansion in the flash tank is introduced into a condenser having surfaces which are continuously wetted by a water-absorbing salt solution. The salt solution used in the condenser may be from any suitable source, but preferably is the salt solution used as an absorption liquid in the absorber and which is circulated through and cooled in the heat exchanger. Water vapor is absorbed by the salt solution or condensed into it as long as the water vapor pressure above the salt solution is lower than the pressure of the vapor released by the expansion from the flash tank. It is thus possible to condense water vapor in a salt solution having a temperature which is about 20.degree. C. or more above the saturation temperature of the water vapor.
It is, accordingly, an object of the present invention to provide a method of producing low air temperatures and low absolute humidities in air conditioning systems.
It is another object of the present invention to improve the efficiency and to lower the energy consumption of air conditioning systems using absorption technique.
These and other objects and advantages of the present invention will be apparent from the following detailed description and the accompanying drawing.